Conventionally proposed boiler systems for combusting a plurality of boilers to generate steam include a boiler system of the so-called proportional control type, for continuously increasing or decreasing a boiler combustion amount to control a steam flow.
For example, Patent Document 1 proposes a control method for proportional control boilers, of operating a plurality of combusting boilers at equivalent load factors, and operating respective combusting boilers at equivalent load factors after the number of combusting boilers varies.